1. Field of the Invention
The present invention relates to a pre-charging system for charging a smoothing capacitor connected in parallel to a switching circuit.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2002-247711 discloses a hybrid vehicle provided with an engine and a motor/generator as traveling drive sources. In this hybrid vehicle, when charging a smoothing capacitor connected to an inverter for converting a DC current of a main battery into an AC current, the motor/generator is driven by the engine to generate an AC current, which is then converted into a DC current by causing the inverter to function as a converter, thereby charging the smoothing capacitor.
When an AC current is converted into a DC current by a converter, and thereafter the DC current is converted into an AC current having a frequency different from that of the original AC current by the inverter, an LC filter comprising a combination of a coil and a capacitor is mounted in order to dull a rectangular wave generated by turning on and off a switching element of an inverter to form a sine wave. However, when the smoothing capacitor is charged, an electric current flows also to the capacitor of the LC filter, and hence there is a problem that the smoothing capacitor cannot be sufficiently charged. Therefore, in the prior art, the complete charging of the smoothing capacitor can be achieved by charging the smoothing capacitor in a state in which the capacitor of the LC filter has been disconnected by an LC relay.
However, if the LC relay is provided on the LC filter in order to completely charge the smoothing capacitor, there is a problem that not only the number of parts is increased, but also the reliability of a pre-charging circuit for charging the smoothing capacitor is reduced, and the performance of the LC filter is reduced due to a loss in the LC relay.